“God give us earlids.”
The starting point
It is essentially a sensible heritage of our evolution that we do not have earlids. Our hearing is the only sensory organ that is active both day and night. But, how do we now deal with the compulsion of “ALWAYS ON”? Unfortunately, in many rooms of our everyday life, appropriate acoustic concepts are all too often not taken into consideration. Our hearing is an extremely sensitive organ with an astonishingly wide range of detection, both in terms of the range of pitches and the volume of sound. In a quiet environment, we can hear the ticking of a wristwatch at some distance, and we can communicate in traffic even with the loudest background noise.
What happens now when closed living, working and leisure spaces fill up with people, with all the associated noise sources: conversations, printer, copier/coffee machines, telephone calls, etc.? In simple terms, a great deal of sound energy is generated, which is distributed like light rays to all sides of the room. Like a mirror, they are continuously reflected on all (boundary) surfaces of the room. During this process, the sound loses part of its energy (volume) each time it hits something, for example a wall, by absorption. This leads to permanent background noise, which remains in the room for a certain time, the reverberation time, even after all sound sources have been switched off. This time depends largely on the volume of the room and the nature (absorption coefficient) of its surfaces. These surfaces have different qualities with regard to their sound absorption. For example, modern design surfaces made of concrete, tiles or glass absorb sound energy only to a very small extent. Fabric-like surfaces such as carpets, curtains and seat upholstery absorb more sound energy, even if only at higher frequencies.
Acoustics in work and leisure rooms
In acoustically untreated rooms with long reverberation times and high noise levels, speakers unconsciously regulate their speech volume depending on their own perception. If this is disturbed by high background noise, they increase their volume. This in turn increases the sound level in the room and causes other people to raise their speech volume as well. This leads to a so-called loudness spiral. Guilty parties are always simultaneously victims. This applies, for example, in the catering trade, equally to the operating personnel and the guest. Both are sources and sufferers of noise. In offices, the most frequent causes of disturbances are conversations between colleagues, telephones ringing and sounds from technical equipment. These types of noise contain both impulses and information. There is no chance of ignoring them, because our mind is evolutionarily trimmed to continuously analyze the acoustic input for usefulness. Symptoms of this daily, disease-causing “continuous sound exposure” include concentration disorders and headaches. A reduced ability to concentrate has an additional negative effect on work results and quality.
Acoustic comfort measures
In order to place our subjective hearing perception on an objective and thus optimizable basis, the room acoustician has a number of standards, guidelines and physical measurement variables at their disposal. The reverberation time as well as other relevant parameters, especially in open-plan offices, can be calculated prognostically or measured. Today, planned, balanced room acoustics are an important part of quality of life. It can be objectively determined and implemented in any room!
Author: Dirk Overzier
Dirk Overzier is a graduate physicist and managing director of a consulting firm specialising in office, object and living room acoustics and a cooperation partner of Remagen.